Risk Assessment of an Existing Metro Tunnel in Close Proximity to New Shield Tunnels following Construction

Table 8

Classification of structural deterioration grades.

Impact degree	Intensity ratio	Safety status of existing tunnel structures
I	≤ 2/3	Unsafe
II	2/3 <  ≤ 4/5	Relatively unsafe
III	4/5 <  ≤ 7/8	Relatively safe
IV	> 7/8	Safe